Preparation of gels from a polyacrylamide and cross-linking agent is known generally in the art. See Chyi-Gang Huang, M.S. Thesis, "A Study of the Gelation of Polyacrylamide Through the Participation of Chromium (III)", 1980, University of Kansas.
Several references teach the use of polyacrylamide gels for oil recovery applications. Polyacrylamide gels are formed by an in situ reaction after injecting the gel components into a subterranean hydrocarbon-bearing formation. In situ formed gels reduce permeability in highly porous regions of the formation thereby facilitating water-flooding and improving hydrocarbon recovery.
U.S. Pat. No. 3,421,584 to Eilers et al injects a gel-forming system comprised of polyacrylamide in particulate form, a cross-linking agent, silicate and a hydrogen ion source such as acid into a formation. The system gels in situ. U.S. Pat. No. 3,785,437 to Clampitt et al sequentially injects alternating aqueous slugs of partially hydrolyzed polyacrylamide and a redox reagent into a subterranean formation. Gelation occurs when the slugs contact and mix in situ. U.S. Pat. No. 3,958,638 to Johnston injects an aqueous solution of partially hydrolyzed polyacrylamide having microencapsulated redox reagent suspended in the solution. As the microcapsules degrade in situ, the redox reagent is released, contacts the polymer, and forms a gel. U.S. Pat. No. 3,782,467 to Hessert generates carbon dioxide from in situ combustion. The carbon dioxide acidifies an injected mixture of polymer and redox reagent to produce a polymer gel in situ. U.S. Pat. No. 3,926,258 to Hessert et al teaches delayed in situ polyacrylamide gelation. Dried polyacrylamide and a reducible cation cross-linking agent are dissolved in a first aqueous solution. A second aqueous solution containing a complexing agent and reducing agent is combined with the first solution. This mixture is injected into the formation where gelation occurs in situ as the complexing agent releases the reducible metal cation.
Polymer gels are also used in drilling fluids as described in U.S. Pat. No. Re. 29,716 to Clampitt. The drilling fluid contains a dilute gel produced from an aqueous solution of partially hydrolyzed polyacrylamide, a reducible metal cation and a reducing agent.
In a non-gelling application, partially hydrolyzed polyacrylamide is a viscosity increasing agent added directly to flooding water as taught by U.S. Pat. No. 3,039,529 to McKennon.
Although partially hydrolyzed polyacrylamide and gels containing the same are used in a number of hydrocarbon production applications described in the above cited art, a process is needed which more effectively utilizes partially hydrolyzed polyacrylamide in hydrocarbon recovery. It is known in the art that gelled polymer can be more effective than ungelled polymer in many subterranean applications. However, in situ gelation processes do not fully exploit the advantages of polymer gels because in situ produced gels are weak and unstable. This is due in large part to insufficient control over the gelation reaction conditions. As such a process is needed whereby a single homogeneous composition can be injected into a subterranean hydrocarbon-bearing formation to significantly improve hydrocarbon recovery from the formation. More specifically a process is needed which maximizes the effectiveness of a polymer gel in hydrocarbon recovery applications, such as face or fracture plugging, permeability reduction or mobility control. The process requires a stable gel which can be produced in a controlled surface environment, yet can be effectively injected into a subterranean formation to perform any of the above noted hydrocarbon recovery-related functions.